Oleg's release of the latest version of ZModeler, the 3D-modeling program that revolutionized the Grand Theft Auto modding world years ago, includes a filter to import .WFT files, the filetype used by GTA IV vehicle models.

The downside is you'll need a registered version of ZModeler to use it, and that'll run you about $60 USD. For the serious modders out there, it's most likely worth the investment so if you're looking to mess around with GTA IV car models, this is your chance!

Although there is not yet a .WFT export tool (meaning you can't yet create GTA IV car mods), this import filter will allow you to take the car models and use them as you please. Simply extract the .WFT files from Spark IV or OpenIV, import them into a registered copy of ZModeler, and change the models as you see fit! For instance, one member of the ZModeler Forum decided to export from ZModeler as DFF and use the Infernus in GTA: San Andreas. The import filter is a huge step forward, and we can probably expect to see full vehicle modding support in the near future!